2. Field of the Invention
The present invention relates to methods and apparatuses for dispensing samples or reagents in analysis apparatuses for use in the fields of chemistry, industry, clinical technology, and biotechnology.
2. Description of the Related Art
Laser desorption/ionization mass spectrometry methods have been performed which apply laser light to samples placed on sample plates mounted in a mass spectrometry apparatus to ionize and analyze the samples. Some of the spectrometry methods employ matrix in creating samples on sample plates, while other spectrometry methods employ no matrix.
The methods which combine such spectrometry methods employing matrix and a time of flight mass spectrometry apparatus are called MALDI-TOF (matrix-assisted laser desorption/ionization mass spectrometry-time of flight) mass spectrometry methods. In MALDI-TOFs, a test sample is dripped onto sample plates along with a matrix solution and detection is conducted after drying them.
On the other hand, there has been suggested a mass spectrometry method which utilizes a small-quantity dispensing technique using piezo devices for causing various reactions on membranes and uses the reaction products, wherein as target samples, biomolecules are separated by electrophoresis, transferred to the membranes and solidified in the membranes (see, international publication No. WO98/47006).
As a method for detecting materials spread and solidified on a membrane, there is immunobloting method. The immunobloting method, generally called western bloting method, is a method which spreads protein samples or the like by electrophoresis, solidifying them in a membrane and causing reaction with specific antibodies as probes for the target materials, thus detecting the presence thereof.
A reagent or sample is dispensed onto a target object, such as a sample plate or a membrane secured on a sample plate, with a dispensing mechanism having a piezo device or the like (referred to as a dispensing device). Then, the sample plate, etc., is transferred to another apparatus, such as a mass spectrometry system or other analysis apparatuses or preparation apparatuses, for performing analyses or subsequent processes.
It is necessary at first that a reagent or sample is accurately dispensed only onto the spot spread on a sample plate or a membrane.
It is preferred that the dispensing device is capable of being replaced in the event of clogging of the dispensing device of the dispensing mechanism or in order to enable dispensing other samples or reagents. In such a case, the dispensing device may be displaced from a predetermined position when the dispensing device is newly mounted or replaced.
When a sample plate, onto which a reagent or sample has been dispensed, is transferred to a subsequent analysis apparatus or processing apparatus, it is necessary to know precisely the position to which the reagent, etc., has been dispensed.
It is commonly required to know the position information after processes are applied to a target object, in various analysis apparatuses and processing apparatuses, not only in liquid dispensing apparatuses.
In the field of analysis apparatuses which mainly utilize liquid-phase materials, regardless of samples or reagents, attempts have been made to reduce the amount of solutions used in analyses. This is because reduction of solutions is effective in reducing the waste of important samples and in reducing the amounts of expensive reagents used, and also it is an effective approach for improving the process efficiency of experiments, since the smaller the amounts of solutions used for biochemical reactions, the shorter the time required for completing the reactions.
In order to cause reactions using small amounts of solutions, there is a need for a dispensing apparatus for dispensing small amounts of samples or reagents. Various methods have been put into prace, as methods for dispensing small amounts of liquids, such as methods using a piezoelectric device such as a piezo device, methods using the opening and closing of valves, and methods utilizing air bubbles which are created by locally heating solutions.
In order to dispense small amounts of liquid onto target positions, there is a need for delicate control of various parameters such as the way of voltage application to a piezoelectric device or the opening time and closing time of a valve. In order to optimize the parameters and further to monitor the shapes of dispensed liquid drops for coping with environmental changes or changes in the piezoelectric device with time since it takes a long time to dispense liquid onto plural positions, images of liquid drops formed at the tip end of the dispensing device are captured and monitored by an image capturing device.
FIG. 16 illustrates a conventional dispensing apparatus with an image capturing device for monitoring the tip end of the dispensing head.
Reference numeral 102 denotes a dispensing mechanism for dispensing a reagent and the dispensing mechanism includes a nozzle at its lower end for dripping a small amount of reagent An X-Y table 104 is placed under the dispensing mechanism 102 and a target object, onto which a reagent is to be dispensed, is placed on the X-Y table 104. The X-Y table 104 can be moved in an X direction and a Y direction within a horizontal plane to position the reagent dispensing position on the target object beneath the nozzle of the dispensing mechanism 102.
Reference numeral 106 denotes an image capturing device for monitoring the conditions of liquid drops formed at the nozzle tip end, and a light source 108 is placed opposite to the image capturing device 106 for enabling monitoring using transmitted images.
In order to accurately dispense liquid onto a target dispensing position, it is preferable that the distance between the dispensing nozzle tip end and the target object is small. Therefore, the image capturing device 106 for monitoring the condition of dispensing is horizontally installed, that is to say, installed at the same height as the nozzle tip end.
Furthermore, in order to dispense liquid stably onto a plurality of positions on the target object, the target object is put on a movable table such as an X-Y table 104, as illustrated in FIG. 16.
In order to install the image capturing device 106 horizontally, and, also in order to prevent interference between the X-Y table 104 and the image capturing device 106, it is necessary that the image capturing device 106 is mounted outside the range of movement of the X-Y table 104, which upsizes the apparatus.
As a dispensing apparatus including a piezo chip, there is a dispensing unit including a piezo chip having a downward opening at its discharging portion. Such a piezo chip is configured to discharge liquid drops from its discharging portion when a driving section including a piezo device pushes the liquid charged in a space communicated to the discharging portion.
When small amounts of liquid are dispensed from the piezo chip in such a dispensing apparatus, it is necessary to maintain the condition where liquid is charged to the tip end of the piezo chip and there is no excess liquid at the tip end thereof. Otherwise desired amounts of liquid can not discharged.
Therefore, conventionally, the piezo chip tip end is photographed by a CCD camera, etc., during test dispensation prior to the start of dispensation. Then, the captured image is displayed in an enlarged manner, and liquid is manually charged by referring to the image and, when excess liquid is leaked from the tip end, the liquid is wiped away.
However, with such conventional methods utilizing manual operations, experience was required to successfully achieve the charging of liquid into the piezo chip and there has been difficulty in creating liquid drops with intended sizes.
Dispensation of small amounts of sample liquid or reagent liquid on the order of picoliters to microliters have been performed by piezo systems or syringe systems.
A dispensing apparatus utilizing a piezo system includes a piezo chip 302 having a discharging portion at its tip end, as illustrated in FIG. 17. In the piezo chip 2, a driving section including a piezo device pushes a liquid reservoir communicated to the discharging portion to discharge liquid drops 306 from the discharging portion. In order to control the driving section for discharging liquid drops of a constant size, a piezo dispensing control section 304 is provided. Liquid drops 306 are discharged from the piezo chip 302 according to parameters for driving the piezo device, which are set in the piezo dispensing control section 304.
In a dispensing apparatus utilizing a syringe system, as illustrated in FIG. 18, liquid drops 6 are discharged from a probe 312 connected to a syringe pump 310 by driving a motor 314 for operating the syringe pump 310. A disposable chip 316 at the tip end of the probe 312 may be provided. The chip 316 is replaced for each sample or reagent A syringe dispensing control section 318 controls the driving of the motor 314 so that operation parameters for the syringe pump 310 become equal to set values to discharge liquid drops 306 with a predetermined size.
The condition of discharging is set depending on the properties, such as the viscosity, of the sample or reagent to be discharged. However, the size of discharged liquid drops varies with environmental changes such as the temperature. Furthermore, the smaller the amount of liquid drops, the poorer the quantifying accuracy.
It is an object of the present invention to enable accurately dispensing liquid onto positions to which liquid is to be dispensed.